Problem: $-\dfrac{4}{12} + \dfrac{2}{6} = {?}$
Answer: $ = - {\dfrac{4 \times 1}{12 \times 1}} + {\dfrac{2 \times 2}{6 \times 2}} $ $ = - {\dfrac{4}{12}} + {\dfrac{4}{12}} $ $ = - \dfrac{{4} + {4}}{12} $ $ = \dfrac{0}{12}$